1. Field of the Invention
The present invention relates to reducing the propagation of electromagnetic interference, particularly in the context of heatsinks for integrated circuits.
2. Background of the Related Art
Electromagnetic interference (EMI) is a disturbance that affects an electrical circuit due to electromagnetic radiation. The disturbance may interrupt, obstruct, or otherwise degrade or limit the effective performance of the circuit. Undesirable electromagnetic radiation often originates in integrated circuits (ICs), and is radiated by other structures at a level sufficient to cause interference with other components. A heatsink can be particularly problematic. Due to its large, metallic surface area, a heatsink may serve as an efficient antenna for propagating electromagnetic radiation.
Numerous approaches to reducing EMI are known in the art. One approach to reducing EMI is the use of bypass or “decoupling” capacitors on each active device. The decoupling capacitors are connected across the power supply, as close to the device as possible. Another known approach to reducing noise is to control the rise time of high-speed signals. The rise time may be controlled, for example, using series resistors. VCC filtering may also be used to reduce the amount of radio frequency interference spread via power supply connections. Shielding may be used, at the expense of adding additional components such as RF gaskets.
As a result of integrated circuit clock and data speeds increasing to beyond 1 GHz, the wavelength of the radiation emitted from an IC is on a similar order of magnitude as the physical dimensions of the IC heatsinks. This contributes to the efficiency of the heatsink acting as an antenna for noise on the IC/IC package. Heatsink grounding schemes exist that attempt to address the problem, but these workarounds add cost to a printed circuit board assembly and also consume a substantial portion of the limited space on a circuit board.